Constructed stormwater wetlands (CSWs) are used to address contaminants in urban stormwater such as nitrogen (N) and phosphorus (P), but their performance is variable. Ephemeral CSWs tend to be less effective than perennial CSWs at removing N and P. We asked: How does wetland vegetation and sediment affect nutrient cycling/release from sediment and vegetation in ephemeral CSWs? We focused on two ephemeral urban CSWs in Pocatello, ID, USA, one densely vegetated and the other nearly bare. We rewetted intact cores of dry wetland sediments and, separately, senesced vegetation for 1 week at the end of the summer dry period to assess whether wetland sediments and vegetation acted as sources or sinks of N and P. For both CSWs, there was a pulse of nutrients immediately following rewetting, but the magnitude of that pulse and subsequent changes in nutrient concentrations suggest different processes dominate at each wetland, driven by differences in wetland vegetation and associated sediment characteristics. There was evidence of denitrification between and during events at the vegetated wetland, but larger fluxes of P at this site suggests a tradeoff between denitrification and P release. While the experimental results suggested specific biogeochemical controls, CSW nutrient concentrations during three events were more dynamic and suggested more biogeochemical complexity than that represented in our experiment, both within events and seasonally. Ephemeral CSWs may create unique biogeochemical conditions and require careful design to ensure N and P retention. Managers will also need to consider whether perennial water sources would improve CSW function.

中文翻译：

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干湿地：临时建造的雨水湿地的营养动态

人工雨水湿地 (CSW) 用于解决城市雨水中的污染物，例如氮 (N) 和磷 (P)，但它们的性能是可变的。短暂的 CSW 在去除 N 和 P 方面往往不如多年生的 CSW 有效。我们问：湿地植被和沉积物如何影响短暂 CSW 中沉积物和植被的养分循环/释放？我们专注于美国爱达荷州波卡特洛的两个短暂的城市 CSW，一个植被茂密，另一个几乎光秃秃的。我们重新润湿了干燥湿地沉积物的完整核心，并在夏季干旱期结束时分别对衰老植被进行了 1 周的再润湿，以评估湿地沉积物和植被是否作为 N 和 P 的源或汇。对于两种 CSW，都有一个脉冲重新润湿后立即吸收营养物质，但这种脉冲的幅度和随后的养分浓度变化表明，由于湿地植被和相关沉积物特征的差异，不同的过程在每个湿地中占主导地位。有证据表明植被湿地发生事件之间和事件期间发生了反硝化作用，但该地点较大的 P 通量表明反硝化作用和 P 释放之间存在折衷。虽然实验结果表明特定的生物地球化学控制，但三个事件期间的 CSW 养分浓度更具动态性，并且表明比我们的实验中所代表的生物地球化学复杂性更高，无论是在事件内还是在季节性。短暂的 CSW 可能会产生独特的生物地球化学条件，需要仔细设计以确保 N 和 P 的保留。